1. Field of the Invention
The present invention generally relates to hinge mechanisms and, more particularly, to a hinge mechanism for hinging together housings of a foldable, portable electronic device such as a mobile phone or a PDA (Personal Digital Assistant).
2. Discussion of the Related Art
Portable mobile phones generally have two housings rotatably joined by a type of hinge that allows the housings to fold upon one another. Many such foldable mobile phones have most of the electronics in one housing, called the main housing, and fewer electronics in the other housing, called the cover. Other such foldable mobile phones have all the electronics in the main housing, with the cover serving only to cover a keypad and a display of the main housing. The main housing and the cover are connected together by a hinge mechanism. Generally, the opening or closing of most covers is achieved by means of a cam mechanism and a spring in the hinge mechanism.
A typical hinge mechanism for a foldable mobile phone includes a shaft, an elastic member, a cam and a cam follower. The cam and the cam follower each have a cam surface attached to the other. The cam, the cam follower and the elastic member surround the shaft. The elastic member pushes directly against the cam. The cam follower matches (i.e., mates and operatively connects) with a main housing of the portable mobile phone. In a similar fashion, the cam matches with a cover. When opening the cover, the cam rotates together with the cover, and it rotates relative to the elastic member and the cam follower. Therefore, a large friction exists between the cam and the elastic member.
It can be seen that, a lot of energy is wasted via friction in the above-described hinge mechanism. In addition, it is difficult to open the cover smoothly because of the substantial degree of friction. Further, the friction will result in abrasion, which will shorten the useful lifetime of the hinge mechanism and eventually make the hinge mechanism perform in an unstable manner. Moreover, the cam surfaces of the cam and the cam follower are difficult to manufacture.
What is needed, therefore, is a hinge mechanism which can have a relatively long working lifetime, and which is stable and energy efficient to use and easy to manufacture.